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Southern resident killer whales have not been getting enough to eat since 2018

Southern orcas haven't been getting enough to eat since 2018

A southern resident killer whale. Credit: NOAA, Ocean Wise

The endangered orca population in the south isn’t getting enough to eat, and hasn’t since 2018, a new study from the University of British Columbia (UBC) has found.

The animals have been in energy deficits, averaged over the spring, summer and fall, for six of the past 40 years — meaning the energy they get from food is less than what they use. Three of those six years fell in the most recent years of the study, 2018 to 2020. The average difference in energy is 28,716 calories, or about 17 percent of the daily energy required for an average adult orca, the authors say.

“With the southern population at such a low level, there is a sense of urgency for this kind of research,” said lead author Fanny Couture, a doctoral student at the Institute for the Oceans and Fisheries (IOF) and Ocean Wise. “Both killer whales and Chinook salmon, the southern resident’s primary prey, are important, iconic species off Canada’s western coast. Studying what’s happening to the population can provide solutions, both for southern residents and potentially other orca populations in the future.”

The southern population, which mainly feeds on Chinook salmon, numbered 73 individuals in October 2021, compared to the growing population in the north of about 300. Studies have shown that the growth of the southern population can be stunted by a lack of food .

The researchers analyzed how changes in abundance, age and size of Chinook, coho and chum populations that southern residents prey on in the Salish Sea and on the west coast of Vancouver Island affected the killer whales’ daily food consumption from 1970 to 2020 . for three seasons a year.

The study used estimated declines in the quantity and size of Chinook salmon to show that lower availability of these fish likely led to energy shortages in killer whales. “The years when southern residents experienced energy shortages are also years when other studies report lower population growth and higher death rates for the killer whales,” said study co-author Dr. Villy Christensen, professor at the IOF.

Previous research has shown correlations between the abundance of Chinook salmon and the survival rate and fertility of southern residents. The decline in Chinook salmon abundance can be attributed to many factors, Couture says, including the effects of climate change, greater susceptibility to disease and predation by other animals.

The model also predicted that southern residents would consume more salmon than Chinook in years when Chinook was at a low level, showing that the animals could switch to other salmon species when the abundance of their primary prey diminishes.

Senior author Dr. Carl Walters, professor emeritus at IOF, said commercial fishing for Chinook salmon in Canada was reduced in the late 1990s after observations of declining abundance. “Those declines have continued despite severe fishing restrictions, and a very likely candidate for causing them is the massive increase in the abundance of Steller sea lions since the mid-1980s; those sea lions now consume more fish than all of BC’s commercial fisheries. for all species, combined.”

Nevertheless, the plight for killer whales living in the south may require a reduction in catches of greater Chinook salmon, which are predictors of whether southern residents are deficient in energy, said Dr. Christians. This may include promoting fishing techniques that increase the survival of larger fish.

Other factors that could affect prey availability for southern residents include noise from underwater boats that could affect foraging, Couture says. This could be an area for future research. Researchers could also apply their model to the northern population to determine whether they too have an energy deficit.

The model did not include winter, as it is unclear where southern residents are during the season. The study is published in PLOS ONE

No apparent shortage of prey for orcas in southern Canada during summer in Canadian waters

More information:
Fanny Couture et al, Prey Requirements and Availability for Killer Whales in the Northeast South Pacific, PLOS ONE (2022). DOI: 10.1371/journal.pone.0270523

Provided by the University of British Columbia

Quote: Killer whales living in the south have not been getting enough to eat since 2018 (June 2022, June 27) retrieved June 27, 2022 from https://phys.org/news/2022-06-southern-resident-killer-whales.html

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